Gambling firms do a lot of things to try and remove the player edge, be it as simple as table limits/max bets or cross selling you more profitable games all the way up to refusing any further business for consistent winners. So while mathematically I think you are correct, in reality it can be very difficult to be in the long tail of profitable winners due to random chance.
Half true. The casinos usually put those measures in place to protect the house profit, but they can still win eachother's money.
Like in a roulette for example you have maximum bet size so that a guy with 1 billion dollar cannot martingale itself to infinity and bankrupt the casino.
However if he bets flat, he can still win the other people's money.
I may have misunderstood you, but that's not how roulette works, you don't win the money from the other players but from the house.
You are absolutely right, the max bet on the roulette table helps prevent the martingale system from working and also reduce the variance on house profits. The free drinks keep the player at the table longer etc etc